Mucoid strains of Pseudomonas aeruginosa, which synthesize a unique capsule composed of alginic acid, are frequently isolated from the respiratory tract of patients with cystic fibrosis (CF). Mucoid strains are rarely isolated from other clinical sources or from the environmental and their appearnce in the respiratory tract of patients with CF correlates with increased morbidity and mortality of the disease. I have elected to approach an understanding of the factors responsible for the association between mucoid strains and CF by establishing the genetic basis for alginic acid production and regulation in rho aeruginosa. Available evidence suggests that the genes involved in alginic acid biosynthesis are located at a specific locus on the chromosome. In order to clarify the location of the alginic acid genes and study their genetic regulation, I plan to develop a versatile cloning system in rho aeruginosa and isolate onto plasmids the genes involved in alginic acid biosynthesis. These chromosomal-plasmid hybrids will be employed to form partial diploids for the purpose of enumerating the alginate genes, identifying their phenotypic function, and examining the genetic regulation of this biosynthetic pathway. It is hoped that such fundamental genetic information will provide a foundation for studies designed to generate effective control measures for mucoid rho aeruginosa infections in patients with CF.